Data storage devices employ rotating data storage media such as hard disk drives or moving magnetic tape. In a hard drive, for example, data is written to the disk medium using a write head which generates a high localized magnetic field which aligns magnetic domains within the disk in one of two directions. In some cases, the magnetization direction is up or down relative to the plane of the disk (perpendicular magnetic recording, or PMR). In other cases, the magnetization direction is within the plane of the disk. In all cases, this data may then be read-out with a read head. The write and read heads are typically integrated within a single assembly. To achieve steadily increasing data storage densities (typically measured in bits/inch2), which are now achieving levels near or beyond 1012 bits/in2 (1 Tb/in2), larger numbers of tracks are being written on each disk. Since disk diameters have remained relatively unchanged, this increase in the number of tracks has necessitated the use of narrower tracks, spaced more closely together. In the past, the read heads used to read data from these tracks were typically narrower than the track width so it was practical to achieve good signal-to-noise ratios (SNRs) using a single head to read the data from each track.
However, track widths are now becoming smaller than the widths of practical magnetic read heads (which are fabricated using methods similar to those in semiconductor manufacturing), with the result that a single read head may pick up increasing amounts of inter-track noise (i.e., the head senses data written on the two neighboring tracks to the track which the head is supposed to be reading). A technology called “Two Dimensional Magnetic Recording” (TDMR) is being applied to address this problem through the use of multiple read heads integrated within a single slider assembly. Another term for TDMR is Multiple-Input/Multiple-Output (MIMO) recording. A slider assembly may typically comprise one or more (for TDMR) read heads as well as a write coil, magnetic pole pieces, and in some embodiments thermal fly height control heaters, and optical waveguides or microwave sources.
The predominant sources of noise in the signal were found to be from adjacent track noise and track edge curvature distortion arising from fringing of the write head and from the fact that the slider does not move in a linear radial motion, but rather along an arc. In a TDMR slider, multiple read heads may be configured in various arrangements, either along-track one in front of the other, or side-to-side in a direction perpendicular to the track, or in some other arrangement—details of the configuration of the plurality of read heads within the TDMR slider are not part of the present invention.
With multiple read heads per slider, testing requirements during data storage system manufacturing become more complex. The difficult economics for the data storage device industry, however, require that testing times cannot substantially increase while still maintaining acceptable manufacturing costs. Thus it would be advantageous in a read head testing system to test TDMR sliders in approximately the same time as non-TDMR sliders are tested.
It would also be advantageous in a TDMR slider testing system to test multiple read heads simultaneously, thereby enabling the testing time for each read head within a TDMR slider to remain approximately the same as the testing time for the single read head in a non-TDMR slider.
It would be further advantageous in a TDMR read head testing system to measure any additional noise sources or read-signal coupling between read heads integrated within single sliders, and to perform this additional testing function with minimal increase in the overall testing time per slider.
It would also be advantageous to employ testing structures and methods for multiple read heads which are modifications of existing testing structures and methods employed for testing non-TDMR sliders, thereby minimizing the efforts required to implement TDMR slider testing in manufacturing.
It would also be advantageous to be able to independently set the bias conditions for each head being tested.
It would be further advantageous to configure the testing structures and methods for TDMR sliders to be compatible with also testing non-TDMR sliders, thereby avoiding the need for dedicated TDMR and dedicated non-TDMR slider testing systems within manufacturing.
Additionally, it would be advantageous to have the test structure be able to test sliders with either common lead or separate lead connections.
It would be advantageous to configure a testing system to be compatible with testing multiple read heads in non-TDMR sliders within a single row bar, thereby decreasing overall read head testing times and improving manufacturing efficiencies.